There is widely known a kind of an electrical connector that has a function of preventing disconnection of the electrical connector from a mating connector. For example, Japanese Patent Application Publication No. 2001-214993 describes an electrical connector having a lock ring instead of a nut screwed onto a male screw of a mating connector. The lock ring has plural flexible projecting sections that are pressed in the direction of the center of the lock ring by a coupling sleeve provided at a position corresponding to the outer periphery of the front end of the lock ring and are engaged with the male screw of the mating connector, when the electrical connector is coupled to the mating connector. When only the coupling sleeve is pulled in the direction of disconnecting the electrical connector, force applied to the projecting sections is released and thereby the electrical connector can be disconnected from the mating connector.
However, when an operator disconnects the electrical connector, as described in Japanese Patent Application Publication No. 2001-214993, from the mating connector, the operator, for example, needs to keep the coupling sleeve in the pulled condition with one hand and move the electrical connector with the other hand in the direction of disconnection. Thus, the operator needs to use both hands to disconnect the electrical connector, which deteriorates working efficiency. In addition, when the above electrical connector and the mating connector are coupled to each other, there may be housings where the electrical connector is disconnected from the mating connector due to vibration or unintentional touching of the coupling sleeve by an object.